The invention relates to correcting distortions in optical signals.
In many optical systems, including both optical data systems and optical imaging systems, beam stabilization and beam focus are critical for error-free data transmission or ideal image quality. Beam focus is particularly problematic when optical signals must be transmitted over long ranges, e.g., several miles, which are common in geographical imaging and interplanetary communication applications. Likewise, beam stabilization is difficult to achieve when atmospheric or mechanical jitter exists in the optical data or imaging system. Jitter can result both from movement of the signal source and movement of the signal reception system. For example, human movement is a common source of mechanical jitter in a video recording system, such as a handheld camcorder.
FIG. 1 shows a common optical signal reception system 15, such as a telescope for use in interplanetary communications. The reception system 15 includes one or more curved mirrors 16a, 16b, which together focus an incoming optical signal at a focal point 17. Another mirror 18 is positioned at the focal point 17 to reflect the focused optical signal onto an optical sensor, such as a photodiode 20, in a receiver. In general, conventional reception systems such as this one preserve and even introduce distortions in the optical signals that result from jitter and lack of focus.
Recognition of the above led the inventor to develop an optical signal acquisition system capable of compensating for spatial vibrations in optical signals and automatically focusing the telescope or lens system from which the optical signal is received.
In one aspect, the invention relates to automatically correcting distortion, such as a spatial vibration or a lack of focus, in an optical signal, such as an optical data signal. An optical relay element receives the optical signal from a remote source and directs the optical signal toward a specified target. A photosensor receives a portion of the optical signal and produces an electronic signal that varies with the distortion in the optical signal. Processing circuitry receives the electronic signal from the photosensor, detects variations in the electronic signal caused by the distortion in the optical signal, and generates a control signal in response to the variations. An adjustment mechanism receives the control signal from the processing circuitry and, in response to the control signal, corrects the distortion in the optical signal.
In some embodiments, the adjustment element is coupled to the optical relay element, and in other embodiments it is coupled to the target. Also, a beam splitter may be positioned before the optical relay element to reflect a portion of the optical signal toward the photosensor. An optical delay element may be positioned before the beam splitter and the optical relay element. A second photosensor may be used to receive a portion of the corrected optical signal and to produce a feedback signal that varies with any distortion that remains in the corrected optical signal. The processing circuitry may be used to receive the feedback signal from the second photosensor, to detect variations in the feedback signal caused by the distortion that remains in the corrected optical signal, and to alter the control signal in response to the detected variations.
In other embodiments, a beam splitter may be positioned after the optical relay element to reflect a portion of the corrected optical signal toward the second photosensor. The optical relay element may be a reflective device, such as a mirror. The adjustment element may be used to adjust the position of the reflective device in response to the control signal. The photosensor may include two pairs of position-sensing, Schottky-barrier photodiodes.
In another aspect, the invention relates to automatically compensating for spatial vibration of an optical signal. An optical relay element receives the optical signal from a remote source and directs the optical signal toward a specified target. A photosensor receives a portion of the optical signal and produces an electronic signal that varies as the optical signal moves across the photosensor as a result of the spatial vibration. Processing circuitry receives the electronic signal from the photosensor, processes the electronic signal to determine the extent of the spatial vibration, and generates a control signal in response to the spatial vibration. An adjustment mechanism coupled to the optical relay element receives the control signal from the processing circuitry and, in response to the control signal, adjusts the optical relay element to compensate for the spatial vibration in the optical signal.
In yet another aspect, the invention relates to automatically focusing an optical signal. An optical relay element receives the optical signal from a remote source and focuses the optical signal on a specified target. A photosensor receives a portion of the optical signal and produces an electronic signal that varies with changes in the focus of the optical signal. Processing circuitry receives the electronic signal from the photosensor, processes the electronic signal to determine whether the focus of the optical signal can be improved, and generates a control signal if the focus can be improved. An adjustment mechanism coupled to the optical relay element receives the control signal from the processing circuitry and, in response to the control signal, adjusts the optical relay element to improve the focus of the optical signal.
The invention is useful in a wide variety of applications, including interplanetary communications and video recording systems. For example, optical signals from a space probe several million miles from Earth can be stabilized and focused with nanometer precision, e.g., to a beam size of 0.005 mm2 at the detector, which allows data communication rates of 1 Gbit/sec or greater. Likewise, optical signals in an optical recording system or an optical microscope can be focused and stabilized automatically with nanometer precision. All of this may be accomplished with a simple, passive detection device that requires no applied bias or power source, and therefore that introduces virtually no noise to the signal acquisition environment.
Other embodiments and advantages will become apparent from the following description and from the claims.